The present disclosure relates generally to improving clutch disengagement of a vehicle. In particular, the present disclosure relates to improving clutch disengagement of the vehicle by enabling a clutch piston time to retract.
In power shift transmissions, a centrifugal head may build up in clutches rotating at high speed when they are not engaged. The centrifugal head may generate enough pressure to cause a disengaged clutch to lock up, resulting in two opposing clutches to fight one another. This may lead to reducing functionality in one of the clutches. One way to stop the centrifugal head from building up is to add a port to a tank in the clutch piston. The port may enable the centrifugal head to flow to the tank, thus not building enough pressure to engage the clutch when the clutch is commanded off. When the clutch is commanded on, the piston moving full stroke closes the port. The port is called Centrifugal Head Internal Relief Port, CHIRP. While the port will prevent clutches from engaging at high rotational speeds, it will not allow them to release at high rotational speeds. When a transmission with power shift clutches is shifted, an offgoing clutch is commanded off near the rotational speed at which it self-engages due to the centrifugal head, and the clutch is connected to the output of the transmission, the next higher gear engaging may rapidly accelerate the vehicle. This rapid acceleration may cause the offgoing clutch piston to not retract fast enough to enable the CHIRP valve to open. This condition becomes more prevalent when the transmission oil is cold, and increases the time for the piston to retract. Power shift transmissions that may be used in conjunction with Continuously Variable Transmissions may perform power shifts at a synchronous speed.